Evaporators for vapor cycle refrigeration systems used for cooling, for example, aircraft must be lightweight and insensitive to acceleration forces due to the motion of the aircraft.
While a number of evaporator constructions have been proposed and have been effective for achieving desired cooling results, a common problem of the proposed evaporator constructions resides in the overall size and weight of the systems necessary to achieve the desired cooling, both of which represent significant factors to be considered in constructing an evaporator for use in the aircraft industry.
In, for example, U.S. Pat. No. 4,347,897, a plate type heat exchanger is proposed wherein a heat exchange is effected between fluids through heat transfer plates, with the heat transfer plates serving as heat transfer elements and jet plates each having a number of small holes. One fluid is jetted through the small holes in the jet plates toward the heat transfer plates opposed to the jet plates while the other fluid flows along a respective opposite heat transfer surfaces or is jetted toward the respective opposite heat transfer surfaces in the same manner as the first fluid.
A disadvantage of the above noted proposed construction resides in the fact that the heat exchanger does not contain any extended surfaces and the jet plate does not contribute to the heat transfer. Moreover, the fluid exiting from the jets near the inlet passage interfere with the jets near the outlet passage thereby reducing the overall heat transfer rate.
U.S. Pat. No. 4,368,779 proposes a heat exchanger which includes stacked perforated sheets forming two series of channels for at least two fluids, with the distribution system being provided at each end and including a series of grooves communicating with an external duct and passages passing through a distribution plate and communicating with the external duct.
While the last mentioned proposed arrangement utilizes a plurality of stacked perforated plates for forming channels for hot and cold fluids, the proposed construction does not contemplate the use of jet impingement which is of extreme significance for the balancing of heat transfer on the single-phase side with that on an evaporating fluid of a two-phase side. Furthermore, in the proposed heat exchanger construction, turbulence is induced by the free edges at each level which does not enhance heat transfer in an evaporator structure wherein a transition between the respective plates must be made as soon as possible so that the liquid fill remains in contact with the walls.
An impingement cooling apparatus is proposed in U.S. Pat. No. 4,494,171, wherein jet impingement is used to cool a hot surface; however, this proposed arrangement relates to a single-phase side and is utilized to cool solid objects such as, for example, electronic components, laser mirrors, etc. not to evaporate another fluid in a helical flow passage adjacent to single-phase channels.
In, for example, U.S. Pat. No. 4,645,001, a heat exchanger is proposed utilizing perforated plates for distributing fluid and inducing jets on an external surface of tubes carrying a second fluid; however, the distribution plates, provided with spray holes, do not contribute to any heat transfer effects in the proposed heat exchanger.
Another form of a heat exchanger with staggered perforated plates is proposed in U.S. Pat. No. 4,624,305; however, the heat exchanger is not of a jet impingement type, nor does the patent address the use of the heat exchanger as an evaporator.
U.S. Pat. No. 4,775,007 also proposes a heat exchanger for an air conditioning apparatus which includes a plurality of regular corrugated fins placed in layers at regular pitches so as to form alternate wide and narrow fluid passages between adjacent corrugated fins, each passage having a plurality of small through holes.